When some applications save files, they do not save each file as an individual file. Instead, these applications might save multiple files of varying formats (e.g., documents, PDFs, Powerpoints, diagrams, images, audio, video, etc.) as an entire folder structure, and identify to the platform or operating system in which it is used, that the file, while appearing to the user as a single file, actually contains multiple files or folders.
This behavior may be application specific and/or operating system specific. For example, MAC shops heavily use “packages,” which are technically folders that have a flag such that they appear like a file to users in the user interface on MAC devices. Specifically, MAC applications including Omnigraffle & iWork save files as packages, and in general, MAC applications are themselves stored as packages. However, outside of the native operating system or platform where a flag which indicates that a given represented file actually includes folders and/or multiple files, errors and unexpected behavior can occur and negatively impact user experience or cause data corruption.